(PITTSBURGH) -- Relying on health-care smartphone apps to detect skin cancer can postpone diagnosis and cause harm, a new study has found.

When researchers at the University of Pittsburgh Medical Center tested four popular apps for detecting melanoma -- the most serious form of skin cancer -- they found that on average three of them incorrectly classified 30 percent or more melanomas. The findings were published Wednesday in the Journal of the American Medical Association-Dermatology.

Of the 188 moles the researchers studied, 60 of them had already been diagnosed as melanoma by a board-certified dermatologist. The study found that the accuracy of the apps varied drastically -- the best-performing apps diagnosed cancerous moles correctly 98.1 percent of the time, while the worst-performing detected melanoma only 6.8 percent of the time.

Typically, in employing these apps, users photograph the skin lesions they would like analyzed, and the app generates a response.

"Patients do bring these in and ask about them," Dr. Darrell Rigel, clinical professor of dermatology at NYU Langone Medical Center, told ABC News. "I tell them that the difference between these and 'real' in-office melanoma diagnostic devices is the difference of a toy car versus a real car. One you play with, and the other works."

The app with the highest sensitivity for melanoma detection, the study found, did not use automated algorithms to analyze the images. Instead, the images were sent to board-certified dermatologists, and users received a diagnosis within 24 hours.

None of these apps, though, are not subject to regulatory oversight, and although disclaimers state they are for educational purposes only -- to help users track their lesions, for example -- dermatologists worry that people, particularly those who are lower-income and uninsured, might substitute the apps' findings for medical advice.

"It is very concerning that these apps are used for diagnosis by patients, as it could lead to delay in diagnosis of melanoma, the cancer which is perhaps the most critical in early diagnosis being important for survival," said Rigel.

The U.S. Food and Drug Administration has responded to the explosion of health-related smartphone apps and announced in July 2011 plans to regulate smartphone apps that paired with medical devices the agency already regulates, such as cardiac monitors and radiologic imaging devices. In 2012, Congress passed the FDA Safety and Innovation Act, allowing the FDA to regulate some medical apps on smartphones. But which apps will come under this regulation and which will not remains unclear.

Given their accessibility, these apps could hold tremendous potential once they have been evaluated, said Dr. Meg R. Gerstenblith, an assistant professor in the department of dermatology at Case Western Reserve University.

"If a patient were insistent on using one of these apps," said Gerstenblith, "I would inform him/her that the current study suggests that those apps that involve a board-certified dermatologist evaluating images of lesions may be superior to those that do not employ a board-certified dermatologist to evaluate the lesions."